In a typical cellular radio system, “wireless” user equipment units (UEs) and one or more “core” networks (like the public telephone network or Internet) communicate via a radio access network (RAN). The UEs very often are mobile, e.g., cellular telephones and laptops with mobile radio communication capabilities (mobile terminals). UEs and the core networks communicate both voice and data information via the radio access network.
The radio access network services a geographical area which is divided into cell areas, with each cell area being served by a base station (BS). Thus, a base station can serve one or multiple cells. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. Base stations communicate over a radio or “air” interface with the user equipment units. In the radio access network, base stations are typically connected, (e.g., by landlines or microwave links), to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of its base stations. In turn, the radio network controllers are typically coupled together and coupled to one or more core network service nodes which interface with one or more core networks.
One example of a radio access network is the Universal Mobile Telecommnunications System (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is a wideband code division multiple access (W-CDMA) system.
In W-CDMA technology, a common frequency band allows simultaneous communication between a user equipment unit and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units. Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit at the same time the origination cell continues to service the connection. Since the user equipment is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The UTRAN accommodates both circuit-switched and packet-switched connections. Circuit-switched connections involve a radio network controller communicating with a mobile switching center (MSC) node which in turn is connected to a connection-oriented, external core network like the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). Packet-switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN), which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched core networks like the Internet and X.25 external networks. There are several interfaces of interest in the UTRAN. The interface between the radio network controllers and the core network(s) is termed the “Iu” interface. The interface between two radio network controllers is termed the “Iur” interface. The interface between a radio network controller and its base stations (or node B's) is termed the “Iub” interface. The interface between the user equipment unit and the base stations is known as the “air interface” or the “radio interface.”
Mobility features of a mobile radio communications system can be divided into two areas: radio mobility, which mainly consists of handover, and network mobility, which mainly consists of location management including location updating and paging. The present invention relates to network mobility. There is a tension in the network mobility process between location and paging procedures. The location procedure allows the system to monitor a user equipment's location in order to be able to find that user in case of an incoming call. Location registration is also used to bring the user's service profile near its location and allows the network to provide the services for which the user has subscribed. The paging process sends paging messages to cells where the mobile terminal could be located. Therefore, if the location cost is high, meaning that the user's location knowledge is accurate, the paging cost will be low, and paging messages need only be transmitted to a small number of cells. On the other hand, if the location cost is low, the paging cost will be high, and paging messages will have to be transmitted over a wider area.
Cellular networks often make use of location areas (LAs). FIG. 1 illustrates two location areas LA1 and LA2. LA1 encompasses representative cells C1–C7, and location area LA2 encompasses representative cells C8–C14. A user equipment's location is “known,” if the system knows the location area in which the subscriber is presently located. When the system must establish a communication with the mobile terminal, paging need only occur in the cells of that location area. Although mobile terminals can periodically update their locations with the network, more often location updates are provided when the mobile terminal crosses a location area boundary. This method requires that each base station cell periodically broadcast its identity and the identity of its location area. Each mobile terminal listens to the broadcast information on a cell's broadcast channel and stores the current location area identity. If the received location area identity differs from the one stored by the mobile radio, a location update procedure is triggered by the mobile. However, a problem with location area procedures is the associated signaling overhead.
Location area signaling overhead is particularly problematic in shared network situations. A shared network is a radio access network infrastructure shared by two or more cellular operators, typically to reduce the cost of network buildout and maintenance. FIG. 2 illustrates an example shared network 1 and includes a core network with one or more core network nodes 2 coupled to a radio access network (RAN) 4 which provides radio access service to a geographic coverage area 6. The core network typically has some responsibilities in handling mobile terminal registrations, location area monitoring and updates, and paging.
The geographic coverage area 6 is divided into several representative location areas (LAs), some of which are “owned” or operated by operator A, and some of which are owned or operated by operator B. For example, location area LA-A1 belongs exclusively to operator A, and location area LA-B1 belongs exclusively to operator B. In contrast, location areas LA-A2, owned by operator 2, and LA-B2, owned by operator B, overlap in coverage area.
The responsibilities and tasks for establishing connections to/from a mobile terminal are often divided between the core network 2 and the radio access network 4. For example, in a UMTS network, these tasks are divided between a logical non-access stratum (NAS) and a logical access stratum (AS). NAS signaling does not require substantive inputs from the RAN, while AS signaling does. The non-access stratum is responsible for mobility management for idle mobile terminals on a location area level and on a routing area level. The access stratum is responsible for mobility management for connected mobile terminals on a routing area and cell level. An idle mobile terminal is “on,” registered, and accessible, but is not currently involved in or using a radio connection supported by the RAN. A connected mobile terminal is currently involved in or using a radio connection supported by the RAN. Being “connected,” the radio network knows the location of the mobile terminal on a cell or UTRAN Registration Area (URA) level, and the core network knows that the mobile terminal is connected.
This allocation of responsibility and tasks between NAS (i.e., core network) and AS (i.e., RAN) does not satisfactorily address situations where the radio access network 4 is shared by two competing (or cooperating) operators, such as the operators A and B shown in FIG. 2. When a mobile terminal in a connected mode is leaving a location area to a cell in a new location area, the mobile terminal may not be allowed to enter the new location area if it is configured for/owned by a competing (or cooperating) operator. A solution to this problem is for the mobile terminal to perform a location area update that involves the core network in such a situation. Upon receiving the location area update from the mobile terminal, the core network detects the identification number of the mobile terminal, e.g., its IMSI number, and checks a database maintained by the core network to determine if the mobile terminal is permitted in the new location area. If it is not permitted, the core network rejects the location update, and the mobile terminal looks for an alternative cell. As shown in the geographic coverage area 6 of FIG. 2, the mobile terminal belongs to operator B and is leaving location LA-B1 into a coverage area shared by operators A and B. Even if the mobile is connected (rather than idle), a location update should be performed so that if the mobile terminal selects a cell in location area LA-A2, the core network will reject that request. As a result, the mobile terminal will have to reselect another cell, hopefully an overlapping cell in location area LA-B2.
The difficulty with this comprehensive location area update approach for idle and connected mobiles is that it adds substantial location area registration signaling load/overhead, and in particular, when the network is not shared between different operators. There may not be a need for the core network to know the exact location of a mobile terminal while it is in a connected mode, except for certain circumstances, e.g., the network is being shared by two or more operators. In other words, there may be some situations, such as a shared location area, when the mobile should perform a location area update with the core network. There may be other situations, in shared network and other contexts, where there is no need for a location area update. The present invention resolves the problem of unnecessary location area updates for both idle mode and connected mode mobile radio terminals.
More specifically, the radio access network provides information to a mobile radio terminal indicating a list of one or more geographic coverage areas from which the mobile radio terminal may or may not obtain service. In the preferred example embodiment, a “forbidden” list includes one or more geographic coverage areas from which the mobile radio terminal may not obtain service. The mobile checks the received information when considering whether to request service from a new geographic coverage area, and deternunes whether to select the geographic coverage area depending on that received information. Moreover, the mobile terminal consults that list to determine whether to perform a location area update procedure. In other words, if the list indicates that a new geographic coverage area should not be selected, the mobile terminal does not perform a location area update request for that new coverage area.
From the perspective of the radio access network, the network receives a message from a mobile radio terminal, and in response to that message, sends information indicating a list of geographic coverage areas from which the mobile radio may or may not request service. In a preferred example embodiment, one of those messages may be a first location area update request message sent by the mobile terminal after being powered on. The radio access network in an example, non-limiting embodiment is shared by first and second operators. The information indicates one or more geographic coverage areas belonging to one of the operators that does not provide service to the mobile radio terminal.
The core network, coupled to the radio access network, formulates determines one or more groups of mobile terminals, and generates a list of location areas corresponding to each of the groups. In response to the message received from the mobile terminal, information associated with one of the lists of the location areas is forwarded to the mobile terminal depending upon the group to which the mobile terminal belongs. For example, each group may represent mobile terminals belonging to a network operator, to a mobile subscriber group, etc. More specifically, in receiving the mobile terminal message, the core network may determine the mobile terminal identifier, and analyze the mobile terminal identifier to determine the group to which the mobile terminal belongs. Two or more core networks may coordinate in generating the list.
In a UTRAN example embodiment, the geographic area may be a location area, and the information may be received in a LOCATION AREA UPDATE ACCEPT message in response to the mobile terminal sending to the radio access network a LOCATION AREA UPDATE REQUEST message. Alternatively, that information may be received in a LOCATION AREA UPDATE REJECTION message in response to the mobile's LOCATION AREA UPDATE REQUEST message.
One aspect of the present invention is a location updating message format used by the radio network to provide the geographic coverage area list information to the mobile radio terminal. The location updating message format includes a location updating message type field, a location area identification field, a mobile terminal identification field, and a location area field indicating location areas that the mobile terminal may or may not select. In a preferred example embodiment, the location area field includes a location area forbidden list. This message format may be employed by a LOCATION UPDATING ACCEPT message and/or a LOCATION UPDATING REJECT message. The invention also provides for a location updating request message transmitted from a mobile radio terminal to a radio access network that includes a location updating message type field, a mobile terminal identification field, and a location area list indicator field indicating whether a location area list associated with the mobile terminal is requested to be sent to the mobile terminal.